Originally Posted by coop410silkies
I haven't started fermented feed - yet. When I was making yogurt - a long time ago - I simply stirred a bit of my favorite live culture into milk, poured it into pint jars, and set the jars in my gas oven. The pilot kept them at the right temperature, and the milk became yogurt almost overnight. (When I used raw goat milk adding a live culture was not necessary.) The point, though, is that if you have a gas oven, the warmth from the pilot may be enough to facilitate the fermentation. Oven is pretty small, though.
Another thing you can try is removing the thermostat and heating element from the glass tube of the aquarium heater and substituting a light bulb for the heating coils - sort of like an incubator set up. Takes a thermometer and a bit of doing, but you can heat almost any kind of an enclosure with it. I used old aquarium heaters to heat old aquariums for starting seeds this way, mostly because I could not find suitable cheap thermostats at the time. Nowadays I might use one of those cheap Chinese Arduino things to thermostatically regulate a light bulb in a tub, box, or cabinet, or whatever. Again, like an incubator.
What I've been doing - until I get committed to FF - is pouring milk into a container of Scratch, stirring well, and setting it in a warm place. A small light bulb in a cupboard would probably work well, especially if I monitored the temp until I found the best wattage to use, but I just haven't bothered. The Scratch absorbs the milk, and, after a couple days, begins to have a nice yeasty smell - even without the addition of a starter culture. My girls - and boys - love this stuff, and they eat it all up before it has a chance to freeze.
Well, I'm NOT advising milk-saturated-Scratch - at least not until I've done some experiments similar to your project; all I'm trying to say is that you might have success fermenting feed with other methods of regulating temperature. Your project sounds great, btw, and, if I can find a source of cheap milk, I could easily see myself doing the same thing with my Scratch Stuff. Yet another thing to tweak!